• Mike Brixius

Commodore Universal Power Supply - Part 1 - Planning

Updated: Aug 24

Update Aug-19-2021: This week I have released the first video and an additional blog post detailing the items I settled on for this build. Hopefully the build video will follow next week. The spreadsheet has been updated with pin numbers and wire colors as well.

The first video detailing the reasons this is needed and the parts that will be used

Some of the Parts for the Universal Bench PSU

It seems like a large percentage of the Commodore computers I get have no power supply with them, or even worse, one that will damage the machine. I made a Commodore 64 power supply earlier but now have another model coming without one, so I have decided that what's needed is a bench power supply that will work with any Commodore machine that came with an external power brick. I also thought it would be nice to be able to simultaneously power an external disk drive like the 1541-II.

Power Requirements

I started by cataloging all the Commodore machines that have an external power brick... At least as many as I could think of but I keep finding more to add. From this, I could see that there a total of 5 voltages that are needed for a build that would cover all the models. They are (Listing the model that uses the most current):

  • 5 Volts DC at 5 Amps for an extreme A500/A1200 config plus 1 external drive

  • 9 Volts DC at 1 Amp for the Commodore 16 and 116 (if you want to support these)

  • 12 Volts DC at 1.5 Amps for the A500 and an external drive

  • -12 Volts DC at a measly 0.1 Amps for the Amiga's

  • 9 volts AC at 3 Amps for the early VIC-20s or 1 Amp if you don't need early VICs

This results in 8 total pins (Updated to separate common and ground)

  1. Common

  2. 5V DC

  3. 9V DC (Optional for C16 & C116)

  4. 12V DC

  5. -12V DC

  6. 9V AC phase 1

  7. 9V AC phase 2

  8. Ground

The project can be simplified (and cost reduced) quite a bit if you forgo support for the Early VIC-20s, C16, and C116. The C16 and C116 in particular just take a 9V DC, 1 Amp wall wart so incorporating it into the project would be trivial but pretty pointless. The early VIC-20 support requires a 9V AC, 3 Amp transformer, the only one I have been able to find costs about $20 so that adds significantly to the cost.

Wall warts that provide 9V AC at 1 amp I find frequently at thrift stores, garage sales and even the local electronics supply store for $1 - $5 and are sufficient for the needs of the later Vic-II, Commodore 64, Plus/4 and and C128.

The Power Chart

Chart of all Commodore models that used an external power supply including voltage and current requirements
Chart of models with power requirements - Updated 8-22-21

Additional Features

In addition to powering any machine I have on my bench I thought it would be nice if it could also provide information on the machines power usage. I found some compact DC voltage and current meters on Amazon that look like they will do the job (edit: 08-21-21 They will not work, they require that each voltage have an isolated common and, since the RT-65B has a single common for all 3 voltages these meters will not work! See a brief explanation video here). I picked up a variety of them so I could see which ones I liked and have settled on a nice little unit that shows both voltage and current in a single display. It didn't hurt that they only Cost about $10 for 3 of them.

The options for AC meters were a great deal more limited. So limited in fact that I would recommend that you just forgo it altogether. The best meter I could find that could handle the low voltages required was large, expensive and limited to voltage only. It is also no longer available so, bleh!

Additional Posts in this Series

Part 1 - This is it!

Part 2 - Commodore Universal Power Supply - Part 2 - Parts

Part 3 - Coming Soon

Recent Posts

See All